Conventionally, in wireless communication in a microwave band and a millimeter waveband, in order to improve quality of communication, high-gain antennas using multiple antennas and multiple wireless circuits are often used. When a high-gain antenna is used, the received power at the receiving side increases and communication distance can be relatively increased.
Here, the configuration of a conventional, typical n-parasitic element-equipped adaptive array antenna 500 shall be described using FIG. 5. It should be noted that FIG. 5 is a diagram showing the configuration of a conventional, typical n-parasitic element-equipped adaptive array antenna.
In FIG. 5, an example of an array antenna including n elements is shown, and the antenna 500 includes parasitic antenna elements 5011 to 501n, fed antenna elements 5021 to 502n, feeder lines 5031 to 503n, and variable phase shifters 5041 to 504n.
Each of the variable phase shifters 5041 to 504n is connected to a corresponding one of the feeder lines 5031 to 503n, and changes the phase of a radio frequency signal transmitted through the corresponding one of the feeder lines 5031 to 503n into an appropriate phase.
The feeder lines 5031 to 503n are designed to have a matching characteristic impedance with the wireless communication apparatus (not shown in the figure) to which the antenna 500 is connected, and are connected to the fed antenna elements 5021 to 502n so as to supply power thereto.
Each of the parasitic antenna elements 5011 to 501n is provided so as to have the same central axis as a corresponding one of the fed antenna elements 5021 to 502n, and the corresponding ones of the fed antenna elements 5021 to 502n and parasitic antenna elements 5011 to 501n are coupled by an electromagnetic field. By changing the respective phases to be changed by the n-system variable phase shifters 5041 to 504n, the phases of the electric fields that are excited at the n-system parasitic antenna elements 5011 to 501n and fed antenna elements 5021 to 502n are individually changed, and radiation pattern of the array antenna is changed.
In this manner, providing parasitic elements in the antenna elements has the advantages of widening the bandwidth and increasing gain, and there are cases where these are used in an array antenna such as that shown in FIG. 5. However, as disclosed in Patent Literature 1 (PTL 1), generally, a fed element and a parasitic element are often arranged so as to have the same central axis in order to increase the coupling intensity between the fed element and the parasitic element.
Furthermore, Patent Reference 2 (PTL 2) discloses a technique of multi-layering parasitic elements and widening the space between the elements to obtain a wide opening area using a small number of fed elements and increase gain.
However, since there is a tradeoff between antenna gain and beam width, the range of the wireless communication angle is narrowed down when attempting to increase the gain of the antenna. In order to compensate for this, a widely used technique is that of an adaptive array antenna (phased array antenna) which is provided with a variable phase shifter in each antenna element, and which changes the beam direction by changing the phases to be changed by the variable phase shifters.